#include <stdio.h>
#include <stdlib.h>

void usage(void) { printf("Usage:...\n"); }

int main(int argc, char **argv) {
    if(argc != 1){ fprintf(stderr, "argc != 1\n"); usage(); exit(1); }

    char str[] = "123a456";
    printf("%d\n", atoi(str)); // 123

    int year = 2025, mon = 2, day = 19;
    char buf[1024] = {0};
    sprintf(buf, "%d-%d-%d", year, mon, day);
    puts(buf); //2025-2-19
    return 0;
}
